Signaling system



.Jan. 4, 1938. w. s. LEMMON SIGNALING SYSTEM Filed June 16, 1934 INVENTOR.

- BY ATTORNEYS.

mmzuumm m. w EEEEE Patented Jan. 4, 1938 PATENT OFFICE srcmnmc SYSTEM Walter S. Lemmon, New York, N. 'Y., assignor to International Business Machines Corporation, -New York, N. Y., a corporation of New York Application June 16, 1934, Serial No: 730,906

. 2 Claims. (01. 178 -88) This invention relates to signaling systems, more particularly to printing telegraph systems and is suitably adaptable to both radio and wire network transmission.

The present invention will be explained in conjunction with a single impulse synchronous transmission system, in which the different characters to be transmitted and received are represented by single impulse signals which are definitely allocated during particular timed intervals. In-

asmuch as the wave shapes of the signals may be. all the same length and amplitude with respect to time, they can be similarly dealt with in trans mission.

This invention consists of a method and means for the transmission and reception of printing telegraph signals, the system being characterized b-y the transformation of the wave shape of the signal during the progress of its transmission and reception. It has been found in the development of this system of transmissionthat a combination of functions is necessaryin order to obtain the greatest reliability and maximum speed and efliciency over long distance radio circuits or wire networks.

As mentioned previously,. broadly, the printing telegraph system embodied in this invention involves the shifting of the character impulse along the axis of a timed scale, the position of the impulse thereon determining the character to be selected. Therefore, it is important to have an impulse of extremely short duration sent out from the printing telegraph transmitter in order to insure accurate timing of the various impulses.

It has been found that this extremely short im pulse is not particularly best suited for future transmission over the network involved to insure maximum efficiency of the system involved. This short impulse signal is then passed through a tank circuit so that it is proportioned to a predetermined value fixed entirely bythe constants of the tank circuit and one found to be most suitable for the transmission to be effected. Upon its reception from theradio or wire network transmitter the impulse may have its crest distorted due'to network characteristics of theline or characteristics of the radio circuit, such an reflections from the Heaviside layer. Usually, however, the front portion of theimpulse wave is undistorted, so that by passing the received impulse through an abbreviator circuit, the particular section of the front portion of the wave may be selected and later used to actuate the selecting devices of the printing telegraph receiver, while the rear portion of .the wave, which is usually distorted, is rejected by the abbreviator circuit;

It is obvious that the abbreviator not only selects a predeterminedportion of the wave'of the received impulse but also reduces the length of the impulse which is of prime importance in allocating the impulse properly on the particular segment of the receiving distributor or commutator in the system. However, this short impulseis not practically suitable'for operation of the character selecting devices, in order then to obtain the maximum power transferred to the selecting devices of the printing receiver, the short impulse is again transformed to a predetermined size and shape most suitable for the particular selecting devices.

It has been found in this system, that a condenser, having a charging time constant matched to the duration of the pulse which then is discharged more slowly through a circuit with fixed constants, is suitable for the purpose.

It is therefore an object of the present invention to provide circuits for transforming the wave shape of the character signal in a particular manner, the particular characteristic shape of the impulse depending on its progression in the transmission and reception cycle. It is obvious thatthis invention is not to be limited to the particular types of signal waves to be disclosed in conjunction with theldescription, since their purpose is solely for graphical illustration of the theoretical progression of transformation of the wave shape during a. transmission or reception cycle. i

Various other objects and advantages of'my invention will be obvious frbm the following particular description of one form of mechanism embodying the invention or from an inspection of the accompanying drawing and the invention also constitutes certain new and novel features of the construction and combination of parts hereinafter set forth and claimed.

In the drawing: v

Fig. 1 shows schematically a system by means of which the invention may be carried out.

Figs. 2 to 8-inclusive are graphs illustrative of the principle employed.

A clear understanding of the invention will be The telegraph transmitter should be so connected that when a character key is depressed erated. A preferred method of obtaining such an impulse of extremely'short duration is genan imfiulse is fully described in' U. S. Patent 1,927,077 issued to G. W. Watson so that the iolable means is adapted to engage the contacts G2 in rather rapid succession, this fact in addition to the narrow construction of the transmitting utator segments 02 cause the impulse to be of extremely short duration. Figure 2 represeats a comparative graphic illustration of the pulse as it is produced by the discharge surge of the condenser Mi coacting with the transmitting commutator us. It is to be understood that an individual condenser id is associated with each character key bar it, and is charged by depressing the key it to close the charging circuit through contact it associated with the key bar ll, battery ill, condenser i l and key bar it. The condenser it is'discharged during a predetermined interval of time when the rotary arm it engages the particular character contact or segment I: through the circuit closed by contact ii and fully described in the aforesaid patent.

The extremely shortimpulse as produced by the printer transmitter units and shown in Fig. 2 is then passed through a tank circuit C in Fig. "1 so that it is increased to a predetermined length. This circuit includes a capacitive reactance l8, inductive reactance id and non-inductive resistance 26 connected as shown and controls a the transformation of the extremely short pulse to a comparative longer pulse as shown in Figure 3.

This procedure helps to overcome slight mechanical inequalities in the transmitter distributing brush system, and it also enables the pulse to attain the proper length best suited for future transmission over the network involved.- In radio circuits the lengthening out of the extremely short pulsein Fig. 2 before feeding it into the wave transmitter serves a useful purpose inasmuch as it then becomes most suitable for the keying circuits at present involved in vacuum tube transmitters in a manner well known to those acquainted in the art. The transformation efi'ect of the circuit as represented at C is fixed entirely 59 by the selection of the L, C, and R constants of the said circuit.

From the tank circuit 0, just described, the pulse isied to the radio or line wave transmitter D, to efiect modulation of the carrier frequency by the particular signal frequency in a manner that is well known and need not be further explained. In Figure 4 the'illustration shows the eii'ect of the signal wave modulating the carrier wave. In Figure 5, the pulse is shown ,as received at E, the usual type wave receiver unit, with its crest distorted due to the network characteristics of the line, or characteristics of the radio circuit, such as reflections from the Heaviside layer. -I'hc front portion of the pulse; however, is usdaily undistorted as shown. In order to remedy the eflects created by the distorted portion of the pulse it is necessary to cut-oil that portion including the distortion. This is done with flhat shall be termed an abbreviator circuit as indicated at F in Fig. 1. The grid oi the thermionic tube 2'l, which is connected in accordance with standard practice for an amplifying stage, is biased at a high negative potential so asto prevent plate current from flowing in the tube when the d is not excited irom some outside source.

if an appreciable amount of current were flowing through the tube this would prevent the s :uof the condenser 22 to the full voltage oi: the B-supply. Through the resistor 28 the condenser 22 charges relatively slowly. When the grid of the tube ii is energised and a positive voltage is impressed thereon, the condenser 22 discharges through the resistor 26, inductive reactance 255 and the tube 29. The length of time required for the said condenser to be'discharged is deteed by the constants of the circuit, namely, the capacitive reactance of condenser 22 and the impedance of the inductive reactance 25 and resistance 26, and the plate resistance of the tube 2i. As soon as the condenser 22 is discharged the plate current in the said circuit is reduced to a negligible amount on account of the high resistance of the circuit due to the resistances 23 and 2d. Thusno appreciable amount of current flows in the said circuit even though the grid of the tube remains positive for a considerable period after the condenser 22 has been discharged. Therefore by selecting the proper L, C, and R. constants impulses of very short duration may be obtained." In this manner not only are extremely short impulses obtained and necessary for extreme accuracy in printing telegraph systems, but the amplitude of the pulses are always a consistent value, which as mentioned above may be of any predetermined value depending on the constants selected.

Referring to Figure 6 an illustration of the pulse obtained from the circuit Just described is shown and which is abbreviated as compared to the pulse shown in the previous Fig. 5. It is to be noted that the distorted portions of the crest of the wave in Fig. 5 do not appear in the pulse from the abbreviator circuit. The output of the said circuit is connected to an amplifier G, the efiect of which is to increase the amplitude of the pulse as shown in Figure 7. The output of the amplifier is then connected to the receiving commutator or distributor H and the printing telegraph receiver J, in a manner fully disclosed in the aforesaid Watson patent. It is understood that the rotary 26 oi the distributor H is rotated in synchro with the rotating arm is of distributor B which is disclosed in the said patent.

, and forth across the corresponding distributor segments or contacts 27 before it shifts 011 the segment, overlapping the adjacent segment and thereby causing an erroneous character to be printed. It is obvious with this allowable tolerance in allocating the impulses on the distributor segments 21, the rotary arms l3 and 28 need not be held in synchronism as accurately as when a longer pulse is used.

However, it has been found that the shortened impulse as shown in Figures 6 and 7 is not efiec: tive, due to its short duration to operate the solenoid 28 connected to the character key bar 29, due to the inductance of the solenoid coil. It is therefore necessary to transform the received pulse again so that the maximum power may be transferred to the solenoid 2| regardless oi the extreme brevity of the original actuating pulse. For this reason the condenser II is used and connected as shown in the diagram, and which is selected to have a charging time constant to match the duration of the pulse. The condenser 30 is first charged by the received impulse and then discharges through the shunt connected solenoid 28 at a slower rate determined by the impedance characteristics 'of the said shunt circuit to effect printing of the selected character.

What is claimed is:

1. A system of the, character described comprising, in combination, a transmitting station having means to transmit successive impulses, a receiving station having means to receive said impulses including a thermionic device having an input circuit including a grid element connected to be energized by the last mentioned impulses and an output circuit including an anode element, said output circuit operated each time the grid element is energized, a resistor and con denser connected in series included in the said output circuit, and means to charge, the condenser during the intervals when the impulses are not impressed upon the grid element, said condenser adapted to be discharged through the output circuit each time the output circuit is operated by the impulses causing the output circuit to be energized for a timed interval less than the period of energization of the input circuit, a recording device, and a circuit connecting the recording device in shunt to said resistor so as to operate the recording device each time the said output circuit is energized.

2. A system of the character described comprising, iri combination, a transmitting station having means to transmit successive impulses, a receiving station having means to receive said impulses including a thermionic device having an output circuit including a grid element connected to be energized by the last mentioned impulses and an output circuit including an anode element, said output circuit operated each time the grid element is energized, a resistor and condenser connected in series included in said output circuit, and means including a resistor and an energy source independent of the signal source to charge the condenser during intervals the impulses are not impressed upon the grid element, said condenser adapted to be discharged through the output circuit each time the output circuit is operated by the impulses causing the output circuit to be energized for a timed interval less than the period. of energization of the input circuit, and a work circuit connected across thefirst'mentioned resistor energized each time the output circuit is energized.

WALTER S. LEMIHON. 

